The present invention relates to a remaining capacity calculation method for a secondary battery, and a battery pack.
A battery pack containing a plurality of secondary batteries is used in various electric devices, and it is widely known that the bodies of the electric devices are arranged so as to notify a user of a remaining capacity of the battery pack by blinking or pulsing light from light emitting diodes and the like. In the case of camcorders (Camcorder: abbreviation for Camera and recorder) for broadcasting stations, for example, their business application require that the remaining capacity be displayed or notified with certain accuracy.
As a method of detecting a charge capacity of the secondary battery, an integration method of obtaining the charge capacity by integrating current or electric power is known. When using the secondary battery (at time of charging, discharging), the voltage and current at that time are measured, and the electric power used is integrated by way of voltage multiplied by current. The remaining capacity rate of the secondary battery is then calculated by obtaining a ratio between the integrated electric power and the dischargeable electric power of the secondary battery.
Japanese Laid-Open Patent Application No. 7-198807 discloses that a battery remaining capacity is calculated based on consumed current of the battery and a temperature of the battery.
However, a disadvantage of the electric power integration method by an integration method is that the error of the remaining capacity calculation is large during a discharge termination phase (final stage of discharge). For example, the electric device may be used even if a remaining capacity is shown as 0%, and even if the remaining capacity is shown as 5%, there is a possibility that the electric device is not available for use. This may constitute a considerably disadvantage for a professional device.
The fact that the remaining capacity calculation error at the final stage of discharge is magnified because of accumulation of measurement errors, generation of reactive electric power due to heat loss and the like, and loss of effective electric power due to a DC impedance (hereinafter simply referred to as DC-Imp) rise of the secondary battery. In the electric power integration method, the integration of the electric power is carried out, with the result that all types of errors are also integrated, so that the error at the final stage of discharge is magnified. In the above-mentioned Japanese Laid-Open Patent Application No. 7-198807, it is difficult to take into account the fact that the error is magnified at the final stage of discharge.